Shape memory alloy actuator arrangement

ABSTRACT

A shape memory alloy actuator arrangement for a movable element supporting a camera lens assembly comprises plural shape memory alloy actuator wires connected between a support structure and the movable element in an arrangement wherein the shape memory alloy actuator wires are arranged, on selective driving, to move the movable element relative to the support structure in any direction orthogonal to the optical axis of the at least one lens. At least one plain bearing bears the movable element on the support structure, allowing movement of the movable element relative to the support structure orthogonal to the optical axis.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/763,751, filed Mar. 27, 2018, now allowed, which is a national stageapplication under 35 U.S.C. § 371 of International ApplicationPCT/GB2016/000174, filed Sep. 29, 2016, which claims priority of GBPatent Application GB 1517202.6, filed Sep. 29, 2015. The disclosures ofwhich are hereby incorporated by reference herein in their entireties.

In one aspect, the present invention relates to a shape memory alloy(SMA) actuator arrangement for a camera lens element that providesmovement orthogonal to the optical axis. More generally, the presentinvention relates to a shape memory alloy (SMA) actuator arrangement fora movable element that provides movement.

In the case of a camera lens element, movement orthogonal to the opticalaxis may be utilised to provide optical image stabilisation (OIS) of animage focused by the camera lens element on an image sensor.

The purpose of OIS is to compensate for camera shake, that is vibrationof the camera apparatus, typically caused by user hand movement, thatdegrades the quality of the image captured by the image sensor. OIStypically involves detecting the vibration by a vibration sensor such asa gyroscope sensor, and controlling, on the basis of the detectedvibration, an actuator arrangement that adjusts the camera apparatus tocompensate for the vibration. Several techniques for adjusting thecamera apparatus are known. OIS by processing of a captured image ispossible in principle but requires significant processing power.Accordingly, there has been developed mechanical OIS in which theoptical system of the camera is adjusted mechanically.

A number of actuator arrangements employing mechanical OIS techniquesare known and applied successfully in relatively large cameraapparatuses, such as digital still cameras, are difficult tominiaturise. Cameras are becoming very common in a wide range ofportable electronic equipment, for example mobile telephones and tabletcomputers, and in many such applications miniaturisation of the camerais important. The very tight packaging of components in miniature cameraapparatuses presents great difficulties in adding OIS actuators withinthe desired package.

In one type of mechanical OIS, a camera lens element is moved orthogonalto the optical axis of the at least one lens. Such a type of OIS will bereferred to herein as “OIS-shift”. OIS-shift has the potential to reducethe size of the overall package for the camera as compared to a type ofOIS in which a camera unit comprising an image sensor and a camera lensassembly for focussing an image on the image sensor is tilted relativeto the support structure around two notional axes that are perpendicularto each other and to the optical axis of the lens assembly, for exampleas disclosed in WO-2010/029316 and WO-2010/089529. This is because onlythe camera lens element is moved and the lateral movement thereofrequires less clearance than tilting the entire camera.

WO-2014/083318 discloses an SMA actuator arrangement that employsOIS-shift. In WO-2014/083318, there is employed a suspension system forsuspending the camera lens element on the support structure that uses atleast one ball to permit movement of the camera lens element relative tothe support structure orthogonal to the optical axis but preventmovement along the optical axis. This provides good performance inoperation. However, balls are difficult to handle in assembly,particularly in a miniature camera lens assembly. This has a negativeimpact of the manufacturing yield. Also, in practice the balls have aminimum size that limits miniaturisation of the arrangement.

It would therefore be desirable to provide an alternative method ofsuspension that does not suffer from these problems, but maintains theoperation performance in permitting movement of the camera lens elementrelative to the support structure. Many types of suspension have highfriction which makes them unsuitable for a camera lens element.

According to a first aspect of the present invention, there is provideda shape memory alloy actuator arrangement for a camera lens element, theshape memory alloy actuator arrangement comprising: a support structure;a movable element for supporting a camera lens assembly comprising atleast one lens having an optical axis; plural shape memory alloyactuator wires connected between the support structure and the movableelement in an arrangement wherein the shape memory alloy actuator wiresare arranged, on selective driving, to move the movable element relativeto the support structure in any direction orthogonal to the opticalaxis; and at least one plain bearing that bears the movable element onthe support structure, allowing movement of the movable element relativeto the support structure orthogonal to the optical axis.

Thus, at least one plain bearing is used to bear the camera lens elementon the support structure, allowing movement of the camera lens elementrelative to the support structure orthogonal to the optical axis. Aplain bearing is a bearing comprising two surfaces in contact with eachother and permitting relative sliding motion. Of course, a plain bearingis a simple type of bearing which is known for use in otherapplications. Inevitably the contact provides friction which adverselyaffects the performance, particularly in a miniature arrangement.However, surprisingly, plain bearings can in fact be used to providegood performance in which the friction is sufficiently low to allowmovement perpendicular to the optical axis. This is possible, in part,because the SMA actuator wires provide a high actuation force comparedto other forms of actuator.

Furthermore, plain bearings may be formed with inherently small sizealong the height of the bearing, that is along the optical axis,especially compared to a suspension system employing balls. This allowsthe size of the arrangement to be reduced along the optical axiscompared to that disclosed in WO-2014/083318.

As the present motion orthogonal to the optical axis of the at least onelens, the plain bearing may comprise conforming surfaces in contact witheach other which are planar. By using a plain bearing comprising planarconforming surfaces, it is possible to avoid contact at a point or alonga line. Such contact at a point or along a line may be disadvantageous,as wear would be concentrated in a small area, which could over timecause changes in the area of contact and hence the properties of thebearing. In contrast, the advantage of a plain bearing comprising planarconforming surfaces is that wear is distributed across a larger area,which area remains stable over time.

Similar problems to those described above for a camera lens elementoccur also in the more general case of an SMA actuator arrangement for amovable element of any other type.

Thus, according to a second aspect of the present invention, there isprovided a shape memory alloy actuator arrangement, the shape memoryalloy actuator arrangement comprising: a support structure; a movableelement; at least one shape memory alloy actuator wire connected betweenthe support structure and the movable element in an arrangement whereinthe shape memory alloy actuator wire is arranged, on driving thereof, tomove the movable element relative to the support structure; and at leastone plain bearing that bears the movable element on the supportstructure, allowing movement of the movable element relative to thesupport structure.

In this more general case, the movement may be in a plane in which casethe at least one plain bearing may comprise conforming surfaces that areplanar, or may be rotational in which case the at least one plainbearing may comprise conforming surfaces that are cylindrical sections.

To allow better understanding, an embodiment of the present inventionwill now be described by way of non-limitative example with reference tothe accompanying drawings, in which:

FIG. 1 is a schematic cross-sectional view of a camera apparatusincluding an SMA actuator arrangement;

FIG. 2 is an exploded perspective view of the SMA actuator arrangement;

FIG. 3 is a side view of the SMA actuator arrangement;

FIG. 4 is a cross-sectional view of a plain bearing of the SMA actuatorarrangement;

FIGS. 5 and 6 are side views of flexures of the SMA actuator arrangementin their relaxed and assembled states;

FIG. 7 is a cross-sectional view of an alternative arrangement of plainbearing;

FIGS. 8 and 9 are plan views of alternative arrangements of plainbearings; and

FIGS. 10 to 14 are cross-sectional views of further alternativearrangements of plain bearings.

A camera apparatus 1 that incorporates an SMA actuator arrangement 40 inaccordance with the present invention is shown in FIG. 1, which is across-sectional view taken along the optical axis O. The cameraapparatus 1 is to be incorporated in a portable electronic device suchas a mobile telephone, or tablet computer. Thus, miniaturisation is animportant design criterion.

The camera apparatus 1 comprises a camera lens assembly 20 suspended ona support structure 4 by an SMA actuator arrangement 40 that supportsthe lens assembly 20 in a manner allowing movement of the lens assembly20 relative to the support structure 4 in two orthogonal directions eachperpendicular to the optical axis O.

The support structure 4 is a camera support supporting an image sensor6. The support structure 4 comprises a base 5, the image sensor 6 beingmounted on the front side of the base 5. On the rear side of the base 5,there is mounted an IC (integrated circuit) chip 30 in which a controlcircuit is implemented, and also a gyroscope sensor 31. The supportstructure 4 also comprises a can 7 protruding forwardly from the base 5to encase and protect the other components of the camera apparatus 1.

The camera lens assembly 20 comprises a lens carriage 21 in the form ofa cylindrical body supporting two lenses 22 arranged along the opticalaxis O, although in general any number of one or more lenses 22 may beprovided. The camera apparatus 1 is a miniature camera in which thelenses 22 (or lens 22 if a single lens is provided) have a diameter ofat most 10 mm.

The lens assembly 20 is arranged to focus an image onto the image sensor6. The image sensor 6 captures the image and may be of any suitabletype, for example a CCD (charge-coupled device) or a CMOS (complimentarymetal-oxide-semiconductor) device.

In this example, the lenses 22 are supported on the lens carriage 21 ina manner in which the lenses 22 are movable along the optical axis Orelative to the lens carriage 21, for example to provide focussing orzoom. In particular, the lenses 22 are fixed to a lens holder 23 whichis movable along the optical axis O relative to the lens carriage 21.Although all the lenses 22 are fixed to the lens holder 23 in thisexample, in general one or more of the lenses 22 may be fixed to thelens carriage 21 and so not movable along the optical axis O relative tothe lens carriage 21, leaving at least one of the lenses 22 fixed to thelens holder 23.

An axial actuator arrangement 24 provided between the lens carriage 21and the lens holder 23 is arranged to drive movement of the lens holder21 and lenses 22 along the optical axis O relative to the lens carriage21. The axial actuator arrangement 24 may be any suitable type, forexample being a voice coil motor (VCM) or an arrangement of SMA actuatorwires, such as is described in WO-2007/113478 which is incorporatedherein by reference.

In operation, the camera lens assembly 20 is moved orthogonally to theoptical axis O in two orthogonal directions, shown as X and Y, relativeto the image sensor 6, with the effect that the image on the imagesensor 6 is moved. This is used to provide OIS, compensating for imagemovement of the camera apparatus 1, caused by for example hand shake.

The SMA actuator arrangement 40 will now be described in more detailwith reference to FIGS. 2 and 3, FIG. 2 being an exploded view of theSMA actuator arrangement 40 omitting the SMA actuator wires 80, and FIG.3 being a side view of the SMA actuator arrangement 40 expanded alongthe optical axis O.

The SMA actuator arrangement 40 comprises a support plate 50 that formspart of the support structure 4 and is connected to the base 5. The SMAactuator arrangement 40 further comprises a moving plate 60. In thisembodiment the moving plate 60 is the moving element, but it couldequally form part of a movable element including other components. Themoving plate 60 supports the camera lens assembly 20 and is connected tothe lens carriage 21. The support plate 50 and the moving plate 60 areintegral sheets made of metal, for example steel such as stainlesssteel.

Each of the support plate 50 and the moving plate 60 is provided with acentral aperture aligned with the optical axis O allowing the passage oflight from the camera lens assembly 20 to the image sensor 6.

Movement of the camera lens assembly 20 relative to the supportstructure 4 is driven by a lateral actuation arrangement comprisingplural SMA actuator wires 80 connected between the support structure 4and the movable element. Specifically, the support plate 50 is formedwith crimps 51 and the moving plate 60 is formed with crimps 61, thecrimps 51 and 61 crimping the four SMA actuator wires 80 so as toconnect them to the support plate 50 and the moving plate 60. The SMAwires 80 may be perpendicular to the optical axis O or inclined at asmall angle to the plane perpendicular to the optical axis O. Each ofthe SMA actuator wires 80 is held in tension, thereby applying a forcebetween the support plate 50 and the moving plate 60 in a directionperpendicular to the optical axis O. In operation, the SMA actuatorwires 80 are selectively driven to move the camera lens assembly 20relative to the support structure 4 in any direction orthogonal to theoptical axis O. The overall arrangement of the SMA wires 80 to achievethis is the same as described in WO-2014/083318, as follows.

SMA material has the property that on heating it undergoes a solid-statephase change which causes the SMA material to contract. At lowtemperatures the SMA material enters the Martensite phase. At hightemperatures the SMA enters the Austenite phase which induces adeformation causing the SMA material to contract. The phase changeoccurs over a range of temperature due to the statistical spread oftransition temperature in the SMA crystal structure. Thus heating of theSMA actuator wires 80 causes them to decrease in length.

The SMA actuator wires 80 may be made of any suitable SMA material, forexample Nitinol or another Titanium-alloy SMA material. Advantageously,the material composition and pre-treatment of the SMA actuator wires 80is chosen to provide phase change over a range of temperature that isabove the expected ambient temperature during normal operation and aswide as possible to maximise the degree of positional control.

On heating of one of the SMA actuator wires 80, the stress thereinincreases and it contracts, causing movement of the camera lens element20. A range of movement occurs as the temperature of the SMA increasesover the range of temperature in which there occurs the transition ofthe SMA material from the Martensite phase to the Austenite phase.Conversely, on cooling of one of the SMA actuator wires 80 so that thestress therein decreases, it expands under the force from opposing onesof the SMA actuator wires 80. This allows the camera lens element 20 tomove in the opposite direction.

The SMA actuator wires 80 have an arrangement in a loop at differentangular positions around the optical axis O to provide two pairs ofopposed SMA actuator wires 80 that are perpendicular to each other. Thuseach pair of opposed SMA actuator wires 80 is capable on selectivedriving to move the camera lens element 20 in one of two perpendiculardirections X and Y orthogonal to the optical axis O. As a result, theSMA actuator wires 80 are capable of being selectively driven to movethe camera lens element 20 relative to the support structure 4 to anyposition in a range of movement in two directions orthogonal to theoptical axis O. The magnitude of the range of movement depends on thegeometry and the range of contraction of the SMA actuator wires 80within their normal operating parameters.

The position of the camera lens element 20 relative to the supportstructure 4 perpendicular to the optical axis O is controlled byselectively varying the temperature of the SMA actuator wires 80. Thisis achieved by passing through SMA actuator wires 80 selective drivesignals that provide resistive heating. Heating is provided directly bythe drive current. Cooling is provided by reducing or ceasing the drivecurrent to allow the SMA wire 80 to cool by conduction, convection andradiation to its surroundings.

The drive signals for the SMA actuator wires 80 are generated andsupplied by the control circuit implemented in the IC chip 30.

The control circuit uses the output signals of the gyroscope sensor 31which is a vibration sensor. The gyroscope sensor 31 detects thevibrations that the camera apparatus 1 is experiencing and its outputsignals represent the angular velocity of the camera lens element 20.The gyroscope sensor 31 is typically a pair of miniature gyroscopes, fordetecting vibration around two axes perpendicular to each other and theoptical axis O, although in general larger numbers of gyroscopes orother types of vibration sensor could be used.

The drive signals are generated by the control circuit in response tothe output signals of the gyroscope sensor 31 so as to drive movement ofthe camera lens element 20 to stabilise an image focused by the cameralens element 20 on the image sensor 6, thereby providing OIS. The drivesignals may be generated using a resistance feedback control techniquefor example as disclosed in any of International Patent Application No.PCT/GB2013/051325; International Patent Application No.PCT/GB2013/052959; WO-2012/066285; WO-2012/020212; WO-2011/104518;WO-2012/038703; WO-2010/089529 or WO-2010029316, each of which isincorporated herein by reference.

In addition, the SMA actuator arrangement 40 comprises three plainbearings 100 spaced around the optical axis O to bear the moving plate60 on the support plate 50. Each plain bearing 100 is arranged asfollows and as illustrated in more detail in FIG. 4.

Each plain bearing 100 comprises a bearing member 101. The bearingmember 101 separates the moving plate 60 and the support plate 50, andthe thickness of the bearing members 101 is chosen accordingly. Due tothe simplicity of the bearing members 101, it possible to minimise theseparation and hence the height of the SMA actuator arrangement 40 alongthe optical axis O.

In one alternative, the bearing member 101 is fixed to the support plate50, for example by adhesive. In this case, the bearing member 101 alsobears on the moving plate 60. That is, a surface 102 of the bearingmember 101 on the opposite side from the support plate 50 and a surface103 of the moving plate 60 are planar, conforming surfaces which contactone another.

In another alternative, the bearing member 101 is fixed to the movingplate 60, for example by adhesive. In this case, the bearing member 101also bears on the support plate 50. That is, a surface 104 of thebearing member 101 on the opposite side from the moving plate 60 and asurface 105 of the support plate 50 are planar, conforming surfaceswhich contact one another.

Thus, the contact between the conforming surfaces 102 and 103 or betweenthe conforming surfaces 104 and 105 supports and bears the movable plate60 on the support plate 50, allowing relative motion parallel to theirextent, that is perpendicular to the optical axis O.

The material properties of the conforming surfaces 102 and 103 or theconforming surfaces 104 and 105 are chosen to provide a low friction andlow wear plain bearing. One option is that the conforming surface 102 or104 of the bearing member 101 is coated by a material having suitableproperties. Another option is that the conforming surface 102 or 104 ofthe bearing member 101 is not coated, but instead the material of thebearing member 101 is chosen to have suitable properties. With eitheroption, the other conforming surface 103 or 105 may also be coated witha material having suitable properties, but that is not essential. Wherecoatings are used, the coating has lower friction and/or lower wear thanthe material which is coated. The bearing member 101 or the coating,where used, may be made from a polymer, for example nylon,polytetrafluoroethylene (PTFE) (e.g. Teflon), an acetal (e.g. Delrin) oran Ultra High Molecular Weight Polyethylene (UHMWPE).

Although FIG. 2 illustrates an example having three bearing members 101,in general there may be any number of one or more bearing members 101.Inclusion of at least three bearing members 101 spaced around theoptical axis O assists in providing stable support and many practicalembodiments include three or four bearing members 101.

The total area of contact of the bearing member 101, that is the area ofthe conforming surfaces 102 or 104 of the bearing member 101 summed overall bearing members present, is chosen to control the friction in thebearing.

Surprisingly, the plain bearings 10 can in fact provide good performancewith friction that is sufficiently low to allow movement perpendicularto the optical axis O, having regard to the force applied by the SMAactuator wires. Typically, in order to limit the friction, the totalarea of contact is at most 3 mm², preferably at most 1.5 mm².

Equally, the plain bearings maintain a relatively high total area ofcontact, due to the contact over the conforming surfaces, compared to abearing having a point or line contact. This reduces the impact of wearoccurring over time and changing the area of contact and hence thebearing properties. Typically, the total area of contact is at least 0.1mm², preferably at least 0.2 mm².

In addition, the SMA actuator assembly 40 comprises two flexures 67connected between the support structure and the movable element to actas a biasing arrangement that biases the support structure and themovable element against each other whilst permitting the movement of themovable element relative to the support structure orthogonal to theoptical axis O. The flexures 67 are arranged as follows.

The flexures 67 each extend between the support plate 50 and the movableplate 60. The flexures 67 have a dual purpose of providing a mechanicalfunction as described below and providing electrical connections fromthe support structure 4 to the camera lens assembly 20.

In this example, the flexures 67 are formed integrally with the movableplate 60 at one end thereof and are mounted to the support plate 50 atthe other end thereof. Alternatively, the flexures 67 could be formedintegrally with the support plate 50 and are mounted to the movableplate 60, or else could be separate elements mounted to each of thesupport plate 50 and the movable plate 60. The mounting of the flexures67 may be achieved by soldering which provides both mechanical andelectrical connection.

The flexures 67 are arranged as follows to provide their mechanicalfunction. Each flexure 67 is an elongate beam connected between thesupport structure 4 and the camera lens assembly 20.

The flexures 67, due to their intrinsic resilience, bias the supportstructure 4 and the camera lens element 20 together, the biasing forcebeing applied parallel to the optical axis O. This maintains the contactin the plain bearings 100. At the same time, the flexures 67 may belaterally deflected to permit said movement of the camera lens assembly20 relative to the support structure 4 orthogonal to the optical axis O,to permit an OIS function.

The flexures 67, again due to their intrinsic resilience, provide alateral biasing force that biases the camera lens assembly 20 towards acentral position from any direction around the central position in whichthe optical axis O of the camera lens assembly is aligned with thecentre of the light-sensitive region of the image sensor 6. As a result,in the absence of driving of the lateral movement of the camera lensassembly 20, the camera lens assembly 20 will tend towards the centralposition from any direction around the central position. This ensuresthat the camera apparatus 1 remains functional to capture images, evenin the absence of driving of the SMA actuator wires 80.

The flexures 67 are designed as follows to provide a suitable retainingforce along the optical axis O for the plain bearings 101, and also topermit lateral movement with a lateral biasing force. The magnitude ofthe lateral biasing force is kept low enough as not to hinder OIS,whilst being high enough to centre the camera lens assembly 20 in theabsence of driving.

Each flexure 67 has a cross-section with an average width orthogonal tothe optical axis O is that is greater than its average thicknessparallel to the optical axis O. Each flexure 67 extends in an L-shapearound the optical axis O, it in general being desirable that theangular extent is at least 90° as measured between the ends of theflexure 67.

In the assembled state of the SMA actuator assembly 40, the flexures 67are deflected from their relaxed state to provide a pre-loading forcethat biases the support structure 4 and the movable element together.This is illustrated in FIGS. 5 and 6, wherein FIG. 5 shows the flexures67 in their relaxed state and FIG. 6 shows the flexures 57 in theirassembled state where the flexures are deflected from their relaxedstate by a distance d.

The flexures 67 are made of a suitable material that provides thedesired mechanical properties and is electrically conductive. Typicallythe material is a metal having a relatively high yield, for examplesteel such as stainless steel.

The SMA actuator arrangement 40 shown in FIG. 2 employs a particularconfiguration of plain bearings 100 as an example, but plain bearingsmay be applied in a any other suitable configuration. By way ofnon-limitative example, some alternative configurations of plainbearings will now be described. Such alternative configurations of plainbearings may be applied as alternatives to the plain bearings 100, butwith the SMA actuator arrangement 40 being otherwise as described above.

In FIG. 2, the bearing member 101 is fixed to one of the support plate50 and the moving plate 60, and the other of the support plate 50 andthe moving plate 60 provide a conforming surface which contacts theconforming surface of the bearing member 101. FIG. 7 illustrates analternative in which the plain bearing 100 comprises bearing members 101fixed to both of the support plate 50 and the moving plate 60. In thiscase, the bearing members 101 provide conforming surfaces 106 and 107which contact one another.

In FIG. 2, the bearing members 101 are separate elements. FIG. 8illustrates in plan view an alternative in which the bearing members 101are integrally formed with an annular ring 108 of the same material. Inthis example, the bearing members 101 and the annular ring 108 are fixedto the support plate 50 (but the arrangement could be reversed so thatthe annular ring 108 is fixed to the movable plate 60). The annular ring108 extends around the optical axis O outside the aperture 52 in thesupport plate 50 but inside the aperture 62 in the moving plate 60, sothat the annular ring 108 does not contact the moving plate 60. Thebearing members 101 protrude outwardly of the annular ring 108 beyondthe aperture 61 so that they overlap and bear on the moving plate 60.This arrangement provides an advantage in manufacture that the annularring 108 and bearing members 101 may be formed as an integral element atthe same time, which facilitates manufacture and improves yield.

As an alternative to providing plural plain bearings 100 spaced aroundthe optical axis O, it is possible to use a single plain bearing that isan annular bearing extending around the optical axis O. By way ofexample, FIG. 9 illustrates in plan view a single plain bearing 100 thatis modified to be annular. The plain bearing 100 comprises an annularbearing member 109 fixed to one of the support plate 50 and the movableplate 60 and bears on the other of the support plate 50 and the movableplate 60 (although for clarity the other of the support plate 50 and themovable plate 60 is not shown in FIG. 9). Such an arrangement provides astable support. The annular plain bearing 100 is formed as a singleannular member, which facilitates manufacture and improves yield.

A potential risk with a plain bearing is that wear particles may beformed by wear of the plain bearing and that such wear particles mayobscure the image capture or create mechanical or electrical problemswithin the SMA actuator assembly 40. It is therefore desirable toprovide means for containing wear particles formed at the plain bearing.A variety of such means are possible. There will now be described somenon-limitative examples of means for containing wear particles that maybe applied to any of the plain bearings 100 described above.

FIG. 10 illustrates in cross-section a plain bearing 100 comprising alabyrinth path 111 as a means for containing wear particles. Thelabyrinth path 111 is formed between the support plate 50 and themovable plate 60, by shaping those components.

FIG. 11 illustrates in cross-section a plain bearing 100 comprising atrap 112 comprising an adherent surface 113 as a means for containingwear particles. The trap 112 is formed in a recess 114 in the supportplate 50, but could be formed additionally or instead on the movableplate 60. The recess 113 contains a material 115 providing the adherentsurface 113. The material 115 is chosen to be adherent to the wearparticles. For example, the material may be silicone or an adhesive.

FIG. 12 illustrates in cross-section another plain bearing 100comprising a trap 116 comprising an adherent surface 117 as a means forcontaining wear particles. However, in this case the trap 116 is formedin a recess 118 in the bearing member 101 of the plain bearing 100.Again, the recess 118 contains a material 119 providing the adherentsurface 117. The material 119 is chosen to be adherent to the wearparticles. For example, the material may be silicone or an adhesive.

FIG. 13 illustrates in cross-section a plain bearing 100 comprising awiper portion 120 as a means for containing wear particles. The wiperportion 120 is formed in the member 101 of the plain bearing 100. Inthis example, the bearing member 101 is fixed to the support plate 50and the wiper portion 120 extends to the surface of the movable element60, but this could be reversed. The wiper portion 120 wipes the movableelement and collects wear particles 121.

The arrangements of FIGS. 12 and 13 are effective in containing wearparticles, although the structures do require sufficient height and somay increase the overall height of the SMA actuator assembly along theoptical axis O, albeit to a lesser extent than a suspension systememploying balls.

FIG. 14 illustrates in cross-section a plain bearing 100 having adiaphragm 122 that contains the plain bearing 100 as a means forcontaining wear particles. In this case, the plain bearing 100 comprisesbearing members 101 fixed to both of the support plate 50 and the movingplate 60, so that the bearing members 101 provide conforming surfaces106 and 107 which contact one another, similar to the arrangement shownin FIG. 7. However, in addition, the diaphragm 122 extends around thebearing members 101, thereby containing the plain bearing 100. Thediaphragm 122 may be made of any suitable material, for examplepolyimide.

The invention claimed is:
 1. A shape memory alloy actuator arrangementsuitable for use with a camera lens assembly, the shape memory alloyactuator arrangement comprising: a support element; a movable elementsuitable for supporting a camera lens assembly comprising at least onelens having an optical axis; plural shape memory alloy actuator wiresarranged, on selective driving, to move the movable element relative tothe support element in any direction orthogonal to the optical axis; andat least one bearing comprising conforming surface regions in contactwith each other and allowing sliding movement of the movable elementrelative to the support structure orthogonal to the optical axis.
 2. Ashape memory alloy actuator arrangement according to claim 1, whereinthe conforming surface regions are planar.
 3. A shape memory alloyactuator arrangement according to claim 2, wherein the support plate andmoving plate are each shaped with crimps crimping the shape memory alloyactuator wires.
 4. A shape memory alloy actuator arrangement accordingto claim 1, wherein the support element includes a support plate formedfrom sheet material, and the movable element includes a moving plateformed from sheet material, the bearing being provided between thesupport plate and the moving plate.
 5. A shape memory alloy actuatorarrangement according to claim 4, wherein the at least one bearingcomprises conforming surfaces in contact with each other which areplanar.
 6. A shape memory alloy actuator arrangement according to claim5, wherein the bearing includes a bearing member fixed to one of thesupport plate and the moving plate, one of the conforming surfaces ofthe bearing being a surface of the bearing member.
 7. A shape memoryalloy actuator arrangement according to claim 6, wherein the other ofthe conforming surfaces of the bearing is a surface of the other of thesupport plate and the moving plate.
 8. A shape memory alloy actuatorarrangement according to claim 6, wherein the bearing includes bearingmembers fixed to both of the support plate and the moving plate, theconforming surfaces of the bearing being a surface of each bearingmember.
 9. A shape memory alloy actuator arrangement according to claim6, wherein the or each bearing member is made of a polymer.
 10. A shapememory alloy actuator arrangement according to claim 5, wherein at leastone of the conforming surfaces has a coating having lower frictionand/or lower wear than the material of the conforming surface which iscoated.
 11. A shape memory alloy actuator arrangement according to claim10, wherein the coating comprises a polymer coating.
 12. A shape memoryalloy actuator arrangement according to claim 1, further comprising abiasing arrangement that biases the support element and the movableelement against each other whilst permitting said movement of themovable element relative to the support element orthogonal to theoptical axis.
 13. A shape memory alloy actuator arrangement according toclaim 12, wherein the biasing arrangement is arranged to provide alateral biasing force that biases the movable element towards a centralposition from any direction around the central position.
 14. A shapememory alloy actuator arrangement according to claim 13, wherein thebiasing arrangement comprises at least one flexure.
 15. A shape memoryalloy actuator arrangement according to claim 14, wherein the supportelement includes a support plate formed from sheet material, and themovable element includes a moving plate formed from sheet material andthe at least one flexure is integrally formed with one of the supportplate and the moving plate.
 16. A shape memory alloy actuatorarrangement according to claim 14, wherein the at least one flexure isdeflected from its relaxed state so that it provides a pre-loading forcethat biases the support element and the movable element together.
 17. Ashape memory alloy actuator arrangement according to claim 1, whereinthe bearing further comprises means for containing wear particles formedat the bearing.
 18. A shape memory alloy actuator arrangement accordingto claim 17, wherein the means for containing wear particles comprisesone of: a labyrinth path formed between the support element and themovable element; a trap comprising an adherent surface; a wiper portion;or a diaphragm containing the bearing.
 19. A shape memory alloy actuatorarrangement according to claim 1, wherein the at least one bearing isplural bearings.
 20. A shape memory alloy actuator arrangement accordingto claim 1, wherein the at least one bearing has a total area of contactat least 0.1 mm², preferably at least 0.2 mm².
 21. A shape memory alloyactuator arrangement according to claim 1, wherein the at least onebearing has a total area of contact at most 3 mm², preferably at most1.5 mm².
 22. A shape memory alloy actuator arrangement according toclaim 1, wherein the at least one bearing is a single annular bearingextending around the optical axis.
 23. A shape memory alloy actuatorarrangement according to claim 1, wherein the at least one lens has adiameter of at most 10 mm.
 24. A shape memory alloy actuator arrangementaccording to claim 1, further comprising an image sensor, the cameralens assembly being arranged to focus an image on the image sensor. 25.A shape memory alloy actuator arrangement according to claim 1, furthercomprising a camera lens assembly comprising at least one lens, thecamera lens assembly being supported on the movable element.
 26. A shapememory alloy actuator arrangement according to claim 1, furthercomprising a control circuit for generating drive signals for the shapememory alloy wires.
 27. A shape memory alloy actuator arrangementaccording to claim 26, further comprising a vibration sensor arranged togenerate output signals representative of the vibration of the system,the lateral control circuit being arranged to generate drive signals forthe shape memory alloy actuator wires in response to the output signalsof the vibration sensor for driving the movement of the movable elementto stabilize an image focused by the movable element.
 28. A shape memoryalloy actuator arrangement, the shape memory alloy actuator arrangementcomprising: a support element; a movable element; at least one shapememory alloy actuator wire arranged, on driving thereof, to move themovable element relative to the support element; and at least onebearing comprising conforming surface regions in contact with each otherand allowing sliding movement of the movable element relative to thesupport element.
 29. A shape memory alloy actuator arrangement accordingto claim 28, wherein the conforming surface regions are planar.
 30. Ashape memory alloy actuator arrangement according to claim 28, whereinthe two surfaces of the at least one bearing comprises a polymercoating.
 31. A shape memory alloy actuator arrangement according toclaim 28, wherein the at least one bearing comprises a bearing memberfixed to one of the support structure and the moving element, whereinthe bearing member is made of a polymer.